Had a cheap Igloo cooler that was ok but didn't keep stuff cold for as long as I wanted. The lid on these are hollow so I drilled a bunch of holes just big enough for the nozzle on a can of Minimum Expansion Foam to fit. Very important to use the minimum foam as the others will warp the top. Sprayed it full, let it set them scraped off the extra.
I then bought a roll of foam tape, Frost King brand, used to seal windows, and placed it around the contact surface between the lid and body.
Next I bought 2 snap hinges and put them on the front to snug down the lid.
I got almost a week of ice in the cheap cooler now during the summer if it's kept in the shade like under the deck in 80 degrees.
Cheap cooler plus $10 or so in parts and I have a week of ice